Nb-doped alpha-MnO2 and foamed nickel composite positive electrode material as well as preparation method and application thereof

Abstract

The invention discloses a Nb-doped alpha-MnO2 and foamed nickel composite positive electrode material and a preparation method and application thereof, and belongs to the technical field of supercapacitors and energy storage. The preparation method comprises the following steps: dissolving KMnO4, MnSO4.H2O and niobium oxalate in water to obtain a mixed solution; the foamed nickel and the mixed solution are mixed for hydrothermal reaction, the Nb-doped alpha-MnO2 and foamed nickel composite positive electrode material is obtained, and the problems of low specific capacitance, low voltage window and the like caused by limitation of the electron transfer rate due to low conductivity of MnO2 are solved. And an asymmetric supercapacitor assembled by the prepared Nb-doped alpha-MnO2 and foamed nickel composite positive electrode material and activated carbon AC shows excellent energy storage capability and cycling stability.

Description

Technical Field

[0001] The present invention relates to an Nb-doped α-MnO2@nickel foam composite positive electrode material, a preparation method thereof and an application thereof, belonging to the technical field of supercapacitors and energy storage. Background Art

[0002] With the continuous growth of global energy demand and the increasing emphasis on environmental protection, energy storage technology has become a hot research field. Efficient, green and reliable energy storage technology is crucial for the sustainable utilization of energy. As a new type of energy storage device, supercapacitors have received extensive attention due to their excellent electrochemical performance and clean and green characteristics.

[0003] The electrode material is the core determinant of the performance of supercapacitors. Therefore, it is necessary to find suitable electrode materials to improve the capacitance performance of supercapacitors. Among many pseudocapacitive electrode materials, MnO2 has been widely used due to its high theoretical specific capacitance (1370 F·g -1 ), economy, greenness and other characteristics. However, the low conductivity of MnO2 limits the electron transfer rate, resulting in problems such as low actual specific capacitance, low voltage window, and large capacity attenuation during long-term charge and discharge processes, which limits its application in supercapacitors. To solve the above defects, in the prior art, Ni is doped into MnO2, and the specific capacitance of Ni-MnO2 is 366 F·g -1 at a current density of 1 A·g -1 , Ag is doped into MnO2, and the specific capacitance of Ag-MnO2 is 350 F·g -1 at a current density of 1 A·g -1 , Cu is doped into MnO2, and the specific capacitance of Cu-MnO2 is 313 F·g -1 at a current density of 1 A·g -1 , but the specific capacitance of the above materials has increased less. Patent CN114927354B adopts a nitrogen doping method. By constant voltage electrochemical deposition of MnO2 nanosheets, an MnO2 / NGCF electrode material is prepared; then the MnO2 / NGCF electrode material is placed in ammonia water for nitrogen doping to obtain a nitrogen-doped manganese dioxide / graphene carbon nanotube electrode material. The method has a complicated process, a large batch production cost, and a long production cycle. Patent CN101409152B adopts a ball milling method. By high-energy ball milling, any one of Al, Ti, Ni, and Fe is mixed with manganese dioxide and then placed in a high-energy ball milling tank to obtain a ball mill-prepared element-doped manganese dioxide supercapacitor electrode material. The method has high energy consumption, limited precision, and high maintenance cost, which is not conducive to large-scale production. Summary of the Invention

[0004] In order to overcome the problems in the background art, the purpose of the present invention is to provide a Nb-doped α-MnO2@nickel foam composite cathode material, a preparation method thereof, and an application thereof.

[0005] In order to achieve the above purpose, the present invention is realized through the following technical solutions:

[0006] The first aspect of the present invention provides a preparation method of a Nb-doped α-MnO2@nickel foam composite cathode material, including the following steps:

[0007] (1) Put KMnO4 and MnSO4·H2O into water and stir, then add niobium oxalate and continue to stir to obtain a mixed solution;

[0008] (2) After pre-treating the nickel foam, mix it with the mixed solution for hydrothermal reaction, cool to room temperature, wash and dry to obtain the Nb-doped α-MnO2@nickel foam composite cathode material.

[0009] Preferably, the molar ratio of KMnO4 to MnSO4·H2O is 3:5.

[0010] Preferably, the molar ratio of Nb to MnO2 in the Nb-doped α-MnO2@nickel foam composite cathode material is (0.05 - 0.16):1.

[0011] Preferably, the temperature of the hydrothermal reaction is 160 °C and the time is 16 h.

[0012] Preferably, the pre-treatment includes: sequentially ultrasonic washing with acetone, deionized water, methanol, absolute ethanol, and deionized water, and finally drying to obtain the pre-treated nickel foam.

[0013] More preferably, the frequency of the ultrasonic wave is 35 - 53 kHz, and the ultrasonic time is 15 - 30 min for each.

[0014] More preferably, the drying temperature is 60 °C - 80 °C and the time is 6 h - 8 h.

[0015] Preferably, in the step (1), the stirring speed for adding niobium oxalate is 600 - 800 rpm, and the stirring time is 20 - 40 min.

[0016] The second aspect of the present invention provides a Nb-doped α-MnO2@nickel foam composite cathode material obtained by using the preparation method described in the first aspect above. The composite cathode material uses nickel foam as the matrix, and a Nb-doped α-MnO2 material grows on the matrix.

[0017] The third aspect of the present invention provides the application of the Nb-doped α-MnO2@nickel foam composite cathode material as a cathode in a supercapacitor.

[0018] Advantages of the present invention:

[0019] The preparation method of the present invention successfully prepared the Nb-doped α-MnO2@nickel foam composite cathode material, solving the problems such as low conductivity of MnO2 restricting the electron transfer rate, resulting in low specific capacitance and low voltage window, etc., providing a new idea for the future development of new green energy storage devices with excellent electrochemical performance. And the prepared Nb-doped α-MnO2@nickel foam composite cathode material and activated carbon AC assembled into an asymmetric supercapacitor showed excellent energy storage capacity, with an energy density of 73 Wh·kg within the voltage window of -0.8 - 1.2 V -1 , and a power density of 1003 W·kg –1 . After 1500 cycles at a current density of 9 A·g -1 , the Nb-α-MnO2 / / AC device still maintained 100% of the initial capacitance, showing excellent cycle stability.

[0020] The synthesis process of the present invention is the hydrothermal method, which does not require high-energy-consuming steps such as electroplating and ball mills, is green and environmentally friendly; the raw materials are rich in sources, low in cost, short in production cycle, and simple in production equipment, which is conducive to large-scale production. Description of the drawings

[0021] Figure 1 FE-SEM images of the cathode materials prepared in Example 1 and Comparative Example 1. (a) is the surface FE-SEM image of Nb-α-MnO2@NF prepared in Example 1 under a 20-μm scale bar; (a1) is the surface FE-SEM image of Nb-α-MnO2@NF prepared in Example 1 under a 2-μm scale bar; (b) is the surface FE-SEM image of α-MnO2@NF prepared in Comparative Example 1 under a 20-μm scale bar; (b1) is the surface FE-SEM image of α-MnO2@NF prepared in Comparative Example 1 under a 2-μm scale bar.

[0022] Figure 2 XPS spectrum of Nb-α-MnO2@NF prepared in Example 1 of the present invention.

[0023] Figure 3 CV curves of the cathode materials prepared in Example 1, Example 2, Example 3 and Comparative Example 1 of the present invention at a scanning rate of 60 mV·s -1 .

[0024] Figure 4 CV curve of the cathode material prepared in Example 1 of the present invention under the condition of broadening the voltage window at a scanning rate of 60 mV·s -1 .

[0025] Figure 5 XRD patterns of the cathode materials prepared in Example 1, Example 2 and Comparative Example 1.

[0026] Figure 6 GCD curves of the cathode materials prepared in Example 1, Example 2, Example 3 and Comparative Example 1 of the present invention at a current density of 1 A·g -1 Current density.

[0027] Figure 7 Nyquist plot of the cathode material prepared in Example 1 of the present invention.

[0028] Figure 8 Nb-α-MnO2 / / AC asymmetric supercapacitor based on the material of Example 1 in 1500 charge-discharge cycle life test diagram. Detailed implementation manners

[0029] The present invention will be further described in detail below in conjunction with specific embodiments, but the protection scope of the present invention is not limited thereto.

[0030] Example 1

[0031] A preparation method of Nb-doped α-MnO2@nickel foam composite cathode material, comprising the following steps:

[0032] (1) Ultrasonically wash nickel foam (NF) with methanol, absolute ethanol, and deionized water for 15 min each, the ultrasonic frequency is 53 kHz, and put the washed nickel foam into a drying oven at 60 °C for 6 h.

[0033] (2) Put 0.1896 g of KMnO4 and 0.3364 g of MnSO4·H2O into 40 mL of deionized water and stir magnetically for 30 min, the stirring speed is 600 rpm, and then add 0.0807 g of niobium oxalate and continue stirring for 15 min to obtain a mixed solution.

[0034] (3) Put the pretreated nickel foam (NF) and the mixed solution into an 80 mL stainless steel autoclave with a polytetrafluoroethylene lining, react at 160 °C in a drying oven for 16 h, and let it cool to room temperature after the reaction.

[0035] (4) Ultrasonically wash the product in absolute ethanol and deionized water three times, the ultrasonic time is 15 min, the ultrasonic frequency is 53 kHz, and then put the washed product into a drying oven at 80 °C for 8 h to obtain 0.05 Nb-α-MnO2@nickel foam composite cathode material.

[0036] The FE-SEM diagram of the 0.05 Nb-α-MnO2@nickel foam composite cathode material obtained in this example is as Figure 1 shown, Figure 1In (a) and (a1), the FE-SEM images of the Nb-α-MnO2@NF surface under 20μm and 2μm scales are shown respectively. It can be seen that the Nb-α-MnO2 particles grow uniformly and have a small size, which is beneficial for contact with the electrolyte and can store more ions. From the figure (a1), it can be seen that there is little agglomeration of Nb-α-MnO2 particles, increasing the surface area.

[0037] According to Figure 2 , for the high-resolution Nb 3d spectrum of Nb-MnO2@NF, two characteristic peaks at binding energies of 209.4 eV and 206.6 eV correspond to Nb 5+ 3d 3 / 2 and Nb 5+ 3d 5 / 2 , which matches the Nb 5+ in niobium oxalate, while Nb 5+ 3d 3 / 2 and Nb 5+ 3d 5 / 2 cannot be detected in pure MnO2@NF. Thus, the existence of free Nb can be confirmed, proving that Nb has been successfully doped into the MnO2 crystal structure, and the Nb-doped α-MnO2@nickel foam nanocomposite cathode material has been prepared.

[0038] According to Figure 5 in the XRD spectrum of 0.05Nb-α-MnO2, as the doping amount of Nb 5+ ions increases, it is found that the diffraction peaks of Nb-MnO2 become significantly broader, and the intensity of the characteristic peak of the (001) crystal plane decreases significantly, indicating that the addition of Nb 5+ ions reduces the grain size of MnO2, and the diffraction peak of the (420) crystal plane becomes broadened or even disappears, further indicating the reduction of the grain size. In 0.05Nb-α-MnO2, MnO2 is α-MnO2.

[0039] Example 2

[0040] The only difference between the preparation method of the Nb-doped α-MnO2@nickel foam composite cathode material in this example and that in Example 1 is that: in step (2), the addition amount of niobium oxalate is 0.1452 g, and finally 0.09Nb-α-MnO2@nickel foam composite cathode material is obtained.

[0041] Example 3

[0042] The only difference between the preparation method of the Nb-doped α-MnO2@nickel foam composite cathode material in this example and that in Example 1 is that: in step (2), the addition amount of niobium oxalate is 0.2582 g, and finally 0.16Nb-α-MnO2@nickel foam composite cathode material is obtained.

[0043] Comparative Example 1

[0044] A preparation method of a pure α-MnO2@nickel foam composite positive electrode material, comprising the following steps:

[0045] (1) Ultrasonically wash nickel foam (NF) with methanol, absolute ethanol, and deionized water for 15 min each, the ultrasonic frequency is 35 kHz, and put the washed nickel foam into a drying oven and dry at 60 °C for 6 h;

[0046] (2) Put 0.1896 g of KMnO4 and 0.3364 g of MnSO4·H2O into 40 mL of deionized water and stir magnetically for 30 min, the stirring speed is 600 rpm to obtain a mixed solution;

[0047] (3) Put the pretreated nickel foam (NF) and the mixed solution into an 80 mL polytetrafluoroethylene high-pressure reaction kettle, react at 160 °C in a drying oven for 16 h, and let it cool to room temperature after the reaction;

[0048] (4) Ultrasonically wash the product in absolute ethanol and deionized water three times in sequence, the ultrasonic time is 15 min, the ultrasonic frequency is 35 kHz, and then put the washed product into a drying oven and dry at 80 °C for 8 h to obtain pure α-MnO2, denoted as Pure MnO2.

[0049] The FE-SEM images of the pure α-MnO2@NF positive electrode material obtained in this comparative example are as Figure 1 shown, Figure 1 in which (b) and (b1) are the FE-SEM images of the surface of pure α-MnO2@NF under the scales of 20 μm and 2 μm respectively; it can be seen that compared with Nb-α-MnO2 particles, the pure α-MnO2 particles have more agglomeration and larger size, indicating that the doping of Nb ions can further prevent the growth of MnO2 crystals, and thus achieve more ion storage.

[0050] According to Figure 5 in the XRD spectrum of Pure MnO2, characteristic peaks of 12.84°, 37.24°, and 66.04° typically appear, corresponding to the (110), (211), and (002) crystal planes respectively, which match α-MnO2 (JCPDS No. 44-0141), have a 2×2 tunnel structure, and MnO2 is α-MnO2.

[0051] Comparative Example 2

[0052] A preparation method of a Nb-β-MnO2@nickel foam composite positive electrode material, comprising the following steps:

[0053] (1) The nickel foam (NF) was ultrasonically washed with methanol, absolute ethanol, and deionized water for 15 min each, the ultrasonic frequency was 53 kHz, and the washed nickel foam was placed in a drying oven and dried at 60 °C for 6 h.

[0054] (2) 0.5 g of (NH4)2SO4 and 0.5 g of MnSO4 were successively placed in 60 mL of deionized water and magnetically stirred for 30 min at a stirring speed of 600 rpm, and then 0.5 g of NbCl5 was added to obtain a mixed solution.

[0055] (3) The pretreated nickel foam (NF) and the mixed solution were placed in an 80 mL stainless steel autoclave with a polytetrafluoroethylene lining, and reacted in a drying oven at 180 °C for 12 h. After the reaction, it was allowed to cool to room temperature.

[0056] (4) The product was successively ultrasonically washed three times with absolute ethanol and deionized water, the ultrasonic time was 15 min, and the ultrasonic frequency was 53 kHz. Then the washed product was placed in a drying oven and dried at 60 °C for 8 h to obtain the Nb-β-MnO2@nickel foam composite cathode material. In the Nb-β-MnO2@nickel foam composite cathode material, MnO2 is in the β phase.

[0057] Comparative Example 3

[0058] A preparation method of a Nb-δ-MnO2@nickel foam composite cathode material, comprising the following steps:

[0059] (1) The nickel foam (NF) was ultrasonically washed with methanol, absolute ethanol, and deionized water for 15 min each, the ultrasonic frequency was 53 kHz, and the washed nickel foam was placed in a drying oven and dried at 60 °C for 6 h.

[0060] (2) 1.264 g of KMnO4 and 0.2015 g of MnSO4 were placed in 60 mL of deionized water and magnetically stirred for 30 min at a stirring speed of 600 rpm, and then 1.0 g of NbCl5 was added to obtain a mixed solution.

[0061] (3) The pretreated nickel foam (NF) and the mixed solution were placed in an 80 mL stainless steel autoclave with a polytetrafluoroethylene lining, and reacted in a drying oven at 160 °C for 12 h. After the reaction, it was allowed to cool to room temperature.

[0062] (4) The product was successively ultrasonically washed three times with absolute ethanol and deionized water, the ultrasonic time was 15 min, and the ultrasonic frequency was 53 kHz. Then the washed product was placed in a drying oven and dried at 80 °C for 6 h to obtain the Nb-δ-MnO2@nickel foam composite cathode material. In the Nb-δ-MnO2@nickel foam composite cathode material, MnO2 is in the δ phase.

[0063] Effect Example 1

[0064] 1. Electrochemical performance tests were carried out in a three - electrode system on an electrochemical workstation (DH7001B). In the three - electrode system, the positive electrode materials prepared in Examples 1 - 3 or Comparative Example 1 were used as the working electrode, a platinum sheet as the counter electrode, and a silver / silver chloride (Ag / AgCl) electrode as the reference electrode. Electrochemical tests were carried out in a 1M Na2SO4 electrolyte at room temperature.

[0065] According to Figure 3 It can be observed that for the Nb - α - MnO2 samples prepared in Examples 1 - 3, when the scanning rate is 60 mV·s -1 , the CV curve shows relatively obvious redox peaks. Compared with the pure α - MnO2 prepared in Comparative Example 1, the Nb - doped α - MnO2 exhibits a wider and more stable voltage window (1.2 V) and a larger response current, indicating that the specific capacitance of Nb - α - MnO2 is higher than that of pure α - MnO2.

[0066] According to Figure 4 It can be observed that for the 0.05Nb - α - MnO2@NF composite positive electrode material prepared in Example 1, under the condition of a scanning rate of 60 mV·s -1 , at a potential of 0.8 - 1.2 V, as the voltage window increases, the shape of the CV curve remains almost unchanged, indicating that the 0.05Nb - α - MnO2 material has pseudocapacitive characteristics. A pair of redox peaks appear at a voltage window of approximately 0.76 V and 1.1 V, which can correspond to the oxidation of Mn 2+ to Mn 3+ and the oxidation of Mn 3+ to Mn 4+ and the reduction of Mn 4+ to Mn 3+ and Mn 3+ to Mn 2+ , further indicating that the doping of Nb can enable the conversion between multivalent Mn ions.

[0067] According to Figure 6 It can be observed that for the 0.05Nb - α - MnO2@NF prepared in Example 1, the longest discharge time is approximately 701 s at a current density of 1 A·g -1 ; the specific capacitance of 0.05Nb - α - MnO2@NF reaches 584 F·g -1 at a current density of 1 A·g -1 , having excellent specific capacitance. For the 0.09Nb - α - MnO2@NF prepared in Example 2, the longest discharge time is approximately 445 s at a current density of 1 A·g -1 ; the specific capacitance of 0.09Nb - α - MnO2@NF is 370 F·g -1 at a current density of 1 A·g-1 。The 0.16Nb-α-MnO2@NF prepared in Example 3 has a longest discharge time of approximately 404 s at a current density of 1 A·g -1 ; at a current density of 1 A·g -1 , the specific capacitance of 0.16Nb-α-MnO2@NF is 336 F·g -1 。The pure α-MnO2@NF cathode material prepared in Comparative Example 1 has a discharge time of only 130 s at a current density of 1 A·g -1 , and the specific capacitance of the pure α-MnO2@NF cathode material is 131 F·g -1 at a current density of 1 A·g -1 . It can be seen that the pure α-MnO2 has a short discharge time and a small specific capacitance.

[0068] Table 1

[0069]

[0070] 2. (1) Mix activated carbon AC, carbon black, and polyvinylidene fluoride (PVDF) binder in a mass ratio of 8:1:1, and then add about 0.6 mL of N-methylpyrrolidone (NMP) to it. Mix well to form a gel-like mixture and coat it on a nickel foam sheet. Place the coated nickel foam in an oven and dry it at 60 °C for 8 h. After taking out the nickel foam, press it under a pressure of 10 MPa for 30 s to obtain nickel foam loaded with the electrode material, that is, the electrode sheet, for standby.

[0071] (2) Use the materials prepared in Examples 1-3 or Comparative Examples 1-3 as the positive electrode, activated carbon AC as the negative electrode, and 1 M Na2SO4 as the electrolyte to construct a Nb-MnO2 / / AC asymmetric supercapacitor or MnO2 / / AC asymmetric supercapacitor for electrochemical testing.

[0072] As Figure 7 can be seen, the impedance analysis shown further evaluates the charge transfer kinetics in the asymmetric supercapacitor. The impedance spectrum is a slanted linear shape in the low-frequency region and a semicircle-like shape in the high-frequency region, corresponding to the diffusion Warburg impedance and the interfacial charge transfer resistance (Rct), respectively. A lower Rct value observed from the curve indicates that the Nb-α-MnO2 / / AC ASC device has high conductivity and excellent rate capabilities.

[0073] As Figure 8 can be seen, the Nb-α-MnO2 / / AC asymmetric supercapacitor obtained by using the Nb-α-MnO2 supercapacitor composite cathode material of Example 1 as the positive electrode, the Nb-α-MnO2 / / AC supercapacitor, at 9 A·g -1At a current density, the capacity retention remains 100% after 1500 cycles, showing excellent cycle stability.

[0074] The Nb-α-MnO2 / / AC asymmetric supercapacitor constructed with the materials prepared in Example 2-3 has a capacity retention of also 100% after 1500 cycles at a current density of 9 A·g -1 However, for the pure α-MnO2 nanocathode material prepared in Comparative Example 1, the capacity retention is poor after 1500 cycles at a current density of 9 A·g -1 current density, and the capacity retention is 64%.

[0075] The electronic conductivity and ion diffusion rate of the Nb-α-MnO2@nickel foam composite cathode materials prepared in Examples 1-3 are significantly better than those of the Nb-β-MnO2 and Nb-δ-MnO2@nickel foam composite cathode materials prepared in Comparative Examples 2-3, and while suppressing Mn 3+ distortion, high redox activity is retained. Therefore, for the Nb-β-MnO2 / / AC asymmetric supercapacitor and Nb-δ-MnO2 / / AC capacitor constructed in Comparative Examples 2-3, the capacity retention is low after 1500 cycles at a current density of 9 A·g -1 current density, similar to that of pure α-MnO2. And at a current density of 1 A·g -1 current density, the discharge time and specific capacitance are significantly lower than those in Examples 1-3. The discharge time is about 200 s - 300 s, and the specific capacitance is 200 - 300 F·g -1

[0076] Finally, it should be noted that the above preferred embodiments are only used to illustrate the technical solutions of the present invention and are not restrictive. Although the present invention has been described in detail through the above preferred embodiments, those skilled in the art should understand that various changes can be made in form and details without departing from the scope defined by the claims of the present invention.

Claims

1. A preparation method of Nb-doped α-MnO2@nickel foam composite cathode material, characterized in that: It includes the following steps: (1) Put KMnO4 and MnSO4·H2O into water and stir, then add niobium oxalate and continue stirring to obtain a mixed solution; (2) Pretreat the nickel foam, mix it with the mixed solution for hydrothermal reaction, cool to room temperature, wash and dry to obtain the Nb-doped α-MnO2@nickel foam composite cathode material.

2. The preparation method of the Nb-doped α-MnO2@nickel foam composite cathode material according to claim 1, characterized in that: The molar ratio of the KMnO4 and MnSO4·H2O is 3:

5.

3. The preparation method of the Nb-doped α-MnO2@nickel foam composite cathode material according to claim 1, wherein: In the Nb-doped α-MnO2@nickel foam composite cathode material, the molar ratio of Nb to MnO2 is (0.05 - 0.16):

1.

4. The preparation method of the Nb-doped α-MnO2@nickel foam composite cathode material according to claim 1, characterized in that: The temperature of the hydrothermal reaction is 160°C and the time is 16 h.

5. The preparation method of the Nb-doped α-MnO2@nickel foam composite cathode material according to claim 1, characterized in that: The pretreatment includes: ultrasonically washing with acetone, deionized water, methanol, absolute ethanol, and deionized water in sequence, and finally drying to obtain the pretreated nickel foam.

6. The Nb-doped α-MnO2@nickel foam composite cathode material prepared by the preparation method of the Nb-doped α-MnO2@nickel foam composite cathode material according to any one of claims 1-5, wherein the composite cathode material uses nickel foam as the substrate, and Nb-doped α-MnO2 material grows on the substrate.

7. Application of the Nb-doped α-MnO2@nickel foam composite cathode material according to claim 6 as a cathode in a supercapacitor.

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